Waves

Nature of Waves wA wave transfers energy through matter or space. wWhen waves move through matter, we call the matter a medium. A medium can be solid, liquid, or gas. wWhen energy waves move through a medium, the medium stays in the same place. wIn the ocean, when a wave passes, the water molecules move only in small circles!

Types of Waves : Transverse wA wave in which the medium moves at right angles to the direction of the wave is a transverse wave. wOcean waves and light waves are transverse. wThe crest is the highest point of a transverse wave, and the trough is its lowest point.

Types of waves: longitudinal wA longitudinal wave has the medium move parallel to the direction of the wave. wThe part of a longitudinal wave where the particles of the medium are close together is a compression. wThe part of a longitudinal wave where the particles of the medium are far apart is a rarefaction. wSound travels in longitudinal waves.

Wave properties wWhen you talk about a “big wave,” you are describing the wave’s amplitude. wIf you describe how many waves pass in a given time, you are describing the wave’s frequency. wFor a transverse wave, the distance from crest to crest or trough to trough is a wavelength.  For a longitudinal wave, a wavelength is the distance between compressions or between rarefactions.It is measured in meters. wavelength rarefaction compression wavelength amplitude

Wave amplitude wIf you are observing transverse waves, the amplitude is the vertical distance from the line of origin and the crest OR the line of origin and the trough. wAs you increase a wave’s energy, its amplitude also increases. Low amplitude High amplitude

Wave frequency wThe frequency of a wave is the number of waves that pass a point in a given time. wThe unit for frequency is the Hertz, which means waves per second. Low frequency High frequency

Wave speed wWave speed measures how fast a wave is moving toward you. wWave speed = frequency x wavelength wThe unit used to measure wave speed is meters per second.

Wave interactions: Energy and change wWhen a wave interacts with another wave or with an object, the amount of energy in the wave changes. wThe change in energy affects the wave’s properties. wWhen a wave hits the shore, its amplitude, speed, or wavelength may change. wOther changes that may happen are a change in wave direction, or the wave may break apart and then re-form.

Wave interactions: reflection wReflection happens when a wave bounces off of a surface. wThe angle of the incoming (incident) wave equals the angle of the outgoing (reflected) wave. Incident wave Angle of incidence Normal Reflected wave Angle of reflection

Wave interactions: diffraction wThe bending of a wave as it contacts the edge of a barrier is called diffraction. wWhen waves are diffracted at the edge of a barrier, their wavelengths and frequencies do not change. outgoing wave crests Incoming wave crests

Wave interactions: refraction wWaves can change speed when they pass from one medium to another. wRefraction is the bending of a wave because of a change in speed.

Wave interactions: interference wThe effect of two or more interacting waves is interference. wWhen two crests meet, the result is a larger wave. This is constructive interference. A tidal wave is caused by constructive interference ! ! ! wWhen a crest and a trough meet, the result is a smaller wave. This is destructive interference.